The invention relates to microvalve devices. In a preferred form, the invention concerns electrostatically operated micromachined flow-through microvalve devices.
Electrostatically operated micromachined integrated silicon, multilayered flow-through microvalves are known. Such microvalve devices are fabricated by micromachining processes, known in general in the field of semiconductor chip technology. They have a wide variety of applications, in particular in computer-controlled systems where low voltages are available and high precision is needed. Pneumatic power systems and ink jet printing devices are examples of relevant applications, and in such apparatus many such microvalves may be required. They must be inexpensive, reliable, efficient, small, and fully compatible with electronic interfaces. They must be capable of repeatable, high precision performance, exhibiting sharp flow cutoff and opening characteristics.
In general terms, a microvalve device has a fluid inlet and a fluid outlet on opposite sides of an integrated silicon wafer construction. An element of the construction forms a valve seat, whilst a further element forms a complementary valve closure, this further element being displaceable under action of an electrostatic force to selectively engage and disengage the valve seat, so to respectively close and open a flow path.
These known electrostatically operated microvalves require an extremely close spacing between an electrode arranged to form part of the valve seat and an electrode associated with the valve closure element, over an area that is substantially larger than the flow orifice, in order to obtain effective valve closures against high fluid pressures whilst avoiding excessive operating voltages. An example of an electrostatically operated microfabricated microvalve is disclosed in U.S. Pat. No. 5,244,537, in which device the closing of the orifice of a normally open valve is controlled by way of two electrodes. The microvalve is an integral structure produced on one piece of silicon with the inlet and outlet on opposite sides of the silicon wafer, and the flow rate of the microvalve is limited by the circumference of the single orifice of the valve.
The present invention provides a normally-closed electrostatic microvalve device of multilayer form comprising:
a stationary valve plate layer, having a plurality of fluid flow orifices therethrough;
a moveable valve plate layer, comprising a plurality of valve elements to close the fluid flow orifices of the stationary valve plate layer, one valve element able to move with a degree of independence from the remaining valve elements;
the movable valve plate layer arranged for deflection under an applied electrostatic force from a normal closed position, in which each of said fluid flow orifices of the stationary valve plate layer is closed by a valve element, to an open position in which one or more of the valve elements is displaced from said stationary valve plate layer.
In a preferred form, the movable valve plate layer comprises resilient flexible portions interconnecting the valve elements, enabling a degree of independent movement to each valve element. The valve elements are preferably supported within the device by resilient restoring support means, such as thin beam elements between the valve elements and a surrounding substrate. The resilient flexible portions interconnecting the valve elements and the resilient restoring support means may be provided by a thin membrane layer forming an integral part of the movable valve plate layer.
In a preferred form of the invention, the device includes a base plate layer spaced from said stationary valve plate layer, having at least one inlet fluid flow orifice therethrough, the base plate layer and the stationary valve plate layer defining therebetween an inlet chamber, the movable valve plate layer being disposed for movement within said inlet chamber, and wherein the base plate layer includes a first conductive electrode element and the movable valve plate layer includes a second conductive electrode element such that application of an electrical potential difference between the respective electrode elements creates an electrostatic force on the moveable valve plate layer to activate the microvalve.
Preferably, application of an electrical potential difference applied between said respective electrode elements results in greater electrostatic force on one valve element than on the remaining one or more valve elements. Each valve element may be associated with a portion of said second electrode layer, and the separation between said first and said second electrode element differs for different ones of said portions when the microvalve is in its normal closed configuration. This may be accomplished by disposing the first electrode layer in a stepped configuration across the base plate layer, so to provide the differing separations between said first electrode layer and the different portions of said second electrode layer.
Preferably, the device includes an outlet plate layer spaced from said stationary valve plate layer, having at least one outlet fluid flow orifice therethrough, the outlet plate layer and the stationary valve plate layer defining therebetween an outlet chamber.
The actuation of the microvalve, then, is effected by the application of an input voltage that results in an electrostatic force between the two electrodes. An important advantage of the valve of the present invention is its ability to manage relatively large flow rates using a normal operating voltage of the order of voltage available conventionally in IC operation. This is achieved by the structure of the multivalve elements in a normally closed microvalve device. In the preferred form, a plurality of valve plates open sequentially to overcome the decreasing pressure difference across the valve.